Graphiti

read-only mode of the editor

The read-only mode of the editor can be achieved by using the ConfigurableFeatureProviderWrapper.
It checks whether the ToolBehaviorProvider is an instance of IFeatureCheckerHolder and if so retrieves its FeatureChecker.
For this the FeatureCheckerAdapter can be used.

multiple instances of one diagram

Derive from FileEditorInput and let this class hold the instance path.
Derive from DiagramEditorMatchingStrategy and extend the matching strategy.